The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Engines produce torque by burning a fuel, and discharge surplus thermal energy. Particularly, a coolant absorbs thermal energy as it circulates through an engine, a heater, and a radiator, and releases the thermal energy.
Oil becomes highly viscous at low engine coolant temperatures. With thick oil, friction and fuel consumption increase, and exhaust gas temperatures rise gradually, lengthening the time taken for catalyst activation and causing deterioration in exhaust gas quality. Moreover, it takes a long time to get a heater to function normally, so passengers and a driver will feel cold.
When the engine coolant temperature is excessively high, knocking may occur. If ignition timing is adjusted to suppress knocking, the engine performance may be degraded. In addition, excessive lubricant temperatures may result in poor lubrication.
However, one coolant control valve unit is used in specific regions of an engine, and is a valve that controls a number of cooling elements, like keeping the coolant at high temperatures and other regions at low temperatures.
When controlling the coolant by using one coolant control valve unit, the coolant control valve unit may be fixed and may be not properly operated, in this case, to inhibit the coolant from being overheated, a bypass line and a bypass valve must be separately installed to the coolant control valve unit.
However, as the bypass line and the bypass valve are separately disposed to the coolant control valve unit, a weight is increased, a number of parts is increased, and a volume of the coolant control valve unit is increased. Furthermore, a production cost and a maintenance cost may be increased.